Turbine seal guards

ABSTRACT

The application may further describe a seal guard in a turbine where the turbine include a plurality of circumferentially spaced nozzles, a plurality of circumferentially spaced turbine blades that each include a blade cover, and an opening defined by a trailing edge of the nozzles and a leading edge of the blade covers. The seal guard may include an upstream axial fin positioned at the trailing edge of the nozzles that extends in a downstream direction across at least part of the opening or a downstream axial fin positioned at a leading edge of a blade cover that extends in an upstream direction across at least part of the opening.

TECHNICAL FIELD

This present application relates generally to systems for protecting turbine components from solid particle erosion and deposits. More specifically, but not by way of limitation, the present application relates to systems for providing a seal guard to deflect solid particles away from turbine seal components.

BACKGROUND OF THE INVENTION

Steam and/or gas turbines generally utilize annular seals between stationary and rotating parts to minimize secondary leakage. Preventing or reducing such leakage allows the efficiency of the turbine to be maximized by forcing a greater percentage of the exhaust flow over the turbine blades. However, often there are impurities or solid particles in the working fluid. In general, the solid particles accelerate to high velocities through the diaphragm stage of the turbine (i.e., as they move along the stationary nozzle blades). Moving at these high velocities, the solid particles may cause erosion, degradation, and result in increased surface roughness to any of the downstream turbine components with which it may come in contact, including the annular seals. In addition to erosion, these solid particles also can become affixed to the rotating or stationary components, thus changing flow areas and potentially causing rubbing damage.

The turbine components that reside in the main steam flowpath generally are protected through specialized coatings or mechanical hardening. The components related to the annular seals, however, typically are made from softer materials and are not treated with specialized coatings or mechanically hardened since the softer material is desirable in the event that rubbing between the stationary and rotating components occurs. Solid particles that contact the annular seal components, thus, often cause erosion and degradation to occur. Such erosion includes the flattening or rounding of the overlapping teeth that form the annular seals, which over time leads to performance and potentially larger reliability issues if the structural integrity of the any of teeth is compromised. Solid particles also may become lodged within the annular seal, which, given the rotational velocity of the rotating parts and the tolerances within the seal between the stationary and rotating parts, may cause significant damage to the seal. In such a situation, the solid particle may cause the rotating and stationary surfaces to rub, which may compromise the structural integrity of the annular seal and/or damage the overlapping teeth that form the seal, leading to increased leakage and reduced turbine efficiency.

Accordingly, the annular seals as well as other sensitive components of steam and gas turbines must be better protected from these solid particle impurities. Prior art systems have not satisfactorily addressed this ongoing issue. Thus, there is a need for improved systems for shielding the seals and other components from solid particle impurities moving through the flowpath.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus may describe a system for preventing solid particle erosion in a turbine. The turbine may include turbine blades that include a blade cover and an opening defined by a trailing edge of a nozzle and a leading edge of the blade cover. The system may include at least one of an upstream axial fin positioned at the trailing edge of the nozzle and a downstream axial fin positioned at the leading edge of the blade cover. The trailing edge of the nozzle may include an outer sidewall.

In some embodiments, the upstream axial fin may include a fin that protrudes from the outer sidewall in a downstream direction. The upstream axial fin may extend in a substantially continuous circumferential manner. In other embodiments, the upstream axial fin may include a fin that extends in an axial manner across at least part of the opening.

In some embodiments, the downstream axial fin may include a fin that protrudes from the blade cover in an upstream direction. The downstream axial fin further may include a fin that extends in an axial manner across at least part of the opening. The downstream axial fin may extend in a substantially continuous circumferential manner.

In some embodiments, the system may include both an upstream axial fin and a downstream axial fin. The upstream axial fin and the downstream axial fin may include approximately the same radial position and substantially span the axial distance of the opening. In other embodiments, the downstream axial fin may be positioned slightly more outward radially than the upstream axial fin. The downstream axial fin and the upstream axial fin may overlap axially.

The upstream axial fin may be an integral part of the outer sidewall. In some embodiments, the upstream axial fin may be attached to the outer sidewall by welding or peening.

The system may further include a downstream groove positioned in the leading edge of the blade cover. The upstream axial fin may span the opening and terminate within the downstream groove. In other embodiments, the system further may include an upstream groove positioned in the trailing edge of the nozzle. The downstream axial fin may span the opening and terminate within the downstream groove.

The application may further describe a seal guard in a turbine where the turbine include a plurality of circumferentially spaced nozzles, a plurality of circumferentially spaced turbine blades that each include a blade cover, and an opening defined by a trailing edge of the nozzles and a leading edge of the blade covers. The seal guard may include an upstream axial fin positioned at the trailing edge of the nozzles that extends in a downstream direction across at least part of the opening or a downstream axial fin positioned at a leading edge of a blade cover that extends in an upstream direction across at least part of the opening. In some embodiments, the system may include both the upstream axial fin and the downstream axial fin, and the upstream axial fin and the downstream axial fin may include approximately the same radial position and substantially span the axial distance of the opening. In other embodiments, the downstream axial fin may be positioned slightly more outward radially than the upstream axial fin and the upstream axial fin and the downstream axial fin may overlap axially.

In some embodiments, the system may include a downstream groove positioned in the leading edge of the blade cover. The upstream axial fin may span the opening and terminate within the downstream groove. In other embodiments, the system may include an upstream groove positioned the trailing edge of the nozzle. The downstream axial fin may span the opening and terminate within the upstream groove.

These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic line drawing illustrating a cross-sectional view of an exemplary environment, i.e., a conventional turbine stage, in which an embodiment of the present application may operate.

FIG. 2 is a schematic line drawing illustrating a cross-sectional view of a turbine stage with a seal guard in accordance with an exemplary embodiment of the present application.

FIG. 3 is a schematic line drawing illustrating a cross-sectional view of a turbine stage with a seal guard in accordance with a further alternative embodiment of the present application.

FIG. 4 is a schematic line drawing illustrating a cross-sectional view of a turbine stage with a seal guard in accordance with another alternative embodiment of the present application.

FIG. 5 is a schematic line drawing illustrating a cross-sectional view of a turbine stage with a seal guard in accordance with another alternative embodiment of the present application.

FIG. 6 is a schematic line drawing illustrating a cross-sectional view of a turbine stage with a seal guard in accordance with another alternative embodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, where the various numbers represent like parts throughout the several views, FIG. 1 illustrates a cross-sectional view of an exemplary environment in which an embodiment of the present application may operate, a turbine stage 10. The turbine stage 10 may be a stage within a steam or gas turbine or other type of turbo machinery. The turbine stage 10 may include a plurality of circumferentially spaced nozzles 12. The nozzle 12 may be a stationary component that directs the flow of a working fluid onto a plurality of circumferentially spaced turbine blades 14. The turbine blade 14 may include an airfoil 16, which extends from a base 18. The base 18 of the turbine blade 14 may connect to a rotor (not shown) such that, in operation, the configuration of the airfoil 16 and the flow of working fluid causes the turbine blades 14 to rotate about the rotor, thus converting the energy of the flow of working fluid into mechanical energy.

At the outward radial end of the airfoil 16, each of the turbine blades 14 may be connected to a blade cover 20. The blade cover 20 may be integral to the turbine blade 14 or may be attached thereto pursuant to conventional methods. In general, the blade cover 20 may be a surface or structure at the outward radial end of the airfoil 16 that runs substantially perpendicular to the surface of the airfoil 16. Among other things, the blade covers may prevent working fluid from leaking over the end of the airfoil 16, which is advantageous because working fluid that leaks over the end of the airfoil 16 does less work thereby decreasing the efficiency of the turbine. The blade cover 20 also may be known as a tip shroud or a bucket cover. Each of the blade covers 20 may extend in a circumferential manner toward the blade covers 20 of the neighboring turbine blades 14. Each of the blade covers 20 may abut the two neighboring blade covers 20. In this manner, the blade covers 20 may create an essentially continuous (though segmented) circumferential ring within the turbine. In another type of construction, the blade covers may span multiple turbine blades. These larger blade covers (not pictured) may then abut each other to form the circumferential ring within the turbine. At an outward radial surface 22 of the blade cover 20, one or more cover teeth 24 may be positioned. The cover teeth 24, which also may be known as vernier teeth, may include tapering or step protrusions that point in the outward radial direction from the outward radial surface 22.

Outward radially of the bucket cover 20, the turbine stage 10 further may include a spill strip 26. The spill strip 26 may be a stationary component that includes a series of abutting arcing segments that, upon assembly, create an essentially continuous circumferential ring in the turbine. At an inward radial surface 28 of the spill strip 26, one or more spill strip teeth 30 may be positioned. The spill strip teeth 30, which may be vernier style, hi-lo style, interlocking style, or any other commonly used style of seal teeth, may include tapering or step protrusions that point in the inward radial direction from the inward radial surface 28. The spill strip teeth 30 and the cover teeth 24 may be positioned such that they form a seal 32 between the blade cover 20 and the spill strip 26, which also may be referred to as an annular, hi-lo, interlocking, or vernier seal. More specifically, the spill strip teeth 30 and the cover teeth 24 may form overlapping or interlocking teeth along the axial length of the blade cover 20/spill strip 26 such that a seal is created that limits the axial movement of working fluid in this area. The spill strip 26 may connect or be integral to a turbine casing 34, which may form an outer casing that encloses the turbine. In addition, in other assemblies, the spill strip 26 may be mounted in the casing, a diaphragm blade/ring carrier, or the downstream diaphragm/blade ring.

Working fluid, such as air in a gas turbine or steam in a steam turbine, may flow through the turbine stage 10. Typically, the working fluid flows through a main flowpath of the turbine (i.e., across the nozzles 12 and then across the airfoils 16). The flow of the main flowpath is depicted in FIG. 1 by arrows 36. In conventional turbine design, there is an opening 38 located between the outer trailing edge of the nozzle 12 and the inner leading edge of the blade cover 20. Working fluid may deviate from the main flowpath and flow into opening 38. The direction of such flow is depicted in FIG. 1 by arrow 40. Working fluid that flows into opening 38 then may contact the components associated with the seal 32, including the spill strip teeth 30 and the cover teeth 24.

Certain impurities, which as used herein may include solid particles or other impurities, may be contained in the working fluid. These solid particles may flow within the main flowpath (as depicted by the arrows 36) and contact turbine components within the main flowpath, such as the nozzles 12 and the airfoils 16. As described, components in the main flowpath generally are protected by specialized coatings or mechanical hardening such that contact with solid particles causes little or no erosion or degradation to the components. The solid particles also may flow into the opening 38. The frequency of this occurrence is increased by the relatively large axial distance of the opening 38 (i.e., the axial distance defined by the outer trailing edge of the nozzle 12 and the inner leading edge of the blade cover 20) in conventional turbine design.

In addition, the relatively gradual curvature at the leading edge of the opening 38 fails to provide any obstruction to solid particles flowing into the opening 38. With no such obstruction, the rotational velocity of the turbine blade 14 may act to essentially “sweep” the solid particles into the opening 38. More specifically, the solid particles tend to move radially outward due to the rotation of the turbine blades 14, which increases the likelihood of the solid particles entering the opening 38 given convention turbine design. Note that the leading edge of the opening 38 (i.e., the trailing edge of the nozzle 12) is often defined by an outer sidewall 46 component. In general, turbine nozzle assemblies may be constructed using several methods. A first method includes using a nozzle 12 with an integrally formed outer sidewall 46 and inner sidewall 47. The outer sidewall 46 and the inner sidewall 46 are used to weld the nozzle 12 directly between an outer ring 48 and an inner ring 49. Nozzles of this configuration often are referred to as singlet nozzles. A second method of nozzle assembly (not shown) uses band/ring construction. In this type of assembly, the nozzles are first welded between inner and outer bands, which extend about 180°. Those arcuate bands with welded airfoils are then assembled and welded between inner and outer carrier rings of the stator of the turbine. Under this second method of nozzle assembly, the leading edge of the opening 38 would be defined by the outer band, which is not depicted in the figures. A third method of assembly (not shown) uses one or more large pieces of material out of which the nozzles are machined. This method is sometimes referred to as “bling” construction.

For the sake of simplicity, the leading edge of the opening 38 will be referred to generally herein as the trailing edge of the nozzle 12 and, more specifically, as the trailing edge of the outer sidewall 46. Those of ordinary skill in the art will recognize that the leading edge of the opening 38, when other nozzle assembly configurations are used, may be defined by other components, such as the outer band component discussed above as well as the outer ring 48, the nozzle 12 and/or other stationary components. Reference herein to the trailing edge of the nozzle 12 or outer sidewall 46, thus, is meant to include those other components that may define the leading edge of the opening 38 in the other types of nozzle assembly configurations.

Once in the opening 38, the solid particles may contact components that typically are made from softer materials and are not treated with specialized coatings or mechanically hardened, such as the cover teeth 24 or the spill strip teeth 30. Solid particles that contact these seal 32 components often cause erosion to occur, which, over time, may significantly damage the cover teeth 24 and/or the spill strip teeth 30 such that the performance of the seal 32 is negatively affected and leakage increases. That is, if the teeth become worn and the overlap between the cover teeth 24 or the spill strip teeth 30 is lessened or destroyed, a greater amount of working fluid will be able to leak through the seal 32. Of course, energy is not extracted from working fluid that travels through the seal, thus decreasing the efficiency of the turbine.

Referring now to FIG. 2, there is illustrated an embodiment of a seal guard 50 according to the present application, which is illustrated in conjunction with the turbine stage 10. Those of ordinary skill will recognize that the use of turbine stage 10 is exemplary only and that the seal guard 50 may be used with other turbine stage configurations. The seal guard 50 may include an upstream axial fin 52 that protrudes in a downstream axial direction from the outer sidewall 46 of the nozzle 12. In other embodiments, more than one axial fin 52 may be provided. More specifically, the upstream axial fin 52 may jut in an axial manner from the outer sidewall 46 across the opening 38. In some embodiments, the upstream axial fin 52 may originate from the outer ring 48 (i.e., the upstream axial fin 52 may jut in an axial manner from the outer ring 48 across the opening 38). At its termination, the trailing edge of the upstream axial fin 52 may be located in close proximity to the leading edge of the blade cover 20. The upstream axial fin 52 may span part or all of the axial distance of the opening 38. In some embodiments, as illustrated in FIG. 2, the end of the upstream axial fin 52 may taper to a point 54.

The upstream axial fin 52 may run in a substantially continuous circumferential manner within the turbine. That is, in some embodiments of nozzle construction, the outer sidewalls 46 of neighboring nozzles 12 may abut to form a substantially continuous circumferential ring. The upstream axial fin 52 may be configured on the outer sidewall 46 (i.e., such that it covers the entire circumferential length of the outer sidewall 46) such that the upstream axial fin 52 runs in a continuous manner (though segmented) around the circumference of the turbine. In other embodiments of nozzle construction, the upstream axial fin 52 may run in a continuous manner around the circumference of the turbine due to other aspects of the configuration of the outer sidewall 46 or outer ring 48 construction.

In some embodiments, the seal guard 50 may include a downstream axial fin 58 that protrudes in an upstream direction from the blade cover 20. In other embodiments, more than one downstream axial fin 58 may be included. More specifically, the downstream axial fin 58 may jut in an axial manner from the blade cover 20 across the opening 38. The downstream axial fin 58 may span approximately part or all of the axial distance of the opening 38. In some embodiments, as illustrated in FIG. 2, the end of the downstream axial fin 58 may taper to a point 60.

The downstream axial fin 58 may run in a substantially continuous circumferential manner. That is, the blade cover 20 of neighboring turbine blades 14 may abut to form a substantially continuous circumferential ring. The downstream axial fin 58 may be configured on the blade cover 20 (i.e., such that it covers the entire circumferential length of the blade cover 20) such that the downstream axial fin 58 runs in a continuous manner (though segmented) around the circumference of the turbine.

In some embodiments, a combination of the upstream axial fin 52 and the downstream axial fin 58 may be used such that they substantially span the axial distance of the opening 38. In other embodiments, as illustrated in FIG. 2, the downstream axial fin 58 may be positioned slightly more outward radially than the upstream axial fin 52. Though not shown, in some embodiments, this positioning may allow the upstream axial fin 52 and the downstream axial fin 58 to overlap axially.

The upstream axial fin 52 may be formed using several methods. In some embodiments, the upstream axial fin 52 may be machined per conventional methods as an integral part of the outer sidewall 46 or the outer ring 48. As stated, in some turbines, the upstream edge of the opening 38 may be defined by an outer band. In such cases, the upstream axial fin 52 may be machined as an integral part of the outer band. The upstream axial fin 52 may be made of an alloy steel (such as 12-chrome, stainless steel, or low alloy steel) and may be, but not necessarily, mechanically hardened through flame hardening or other similar mechanical processes. In alternative embodiments, a coating may be used on the upstream axial fin 52 such as those typically used on components in the flow path rather than a mechanical hardening process. The purpose of this mechanical hardening or providing a protective coating would be to allow the upstream axial fin 52 to better resist erosion from the solid particles.

As illustrated in FIG. 3, the upstream axial fin 52 also may be welded onto an outer sidewall 46, or in other cases (not shown), the outer ring 48. As shown, the upstream axial fin 52 may be welded to an outer sidewall 46 that lacks such a component. In such a case, a long tapering piece 70 may be welded to the trailing edge of the outer sidewall 46 such that the upstream axial fin 52 is formed. A weld 72 located at the upward radial surface of the long tapering piece 70 and a weld 74 located at the lower leading edge of the long tapering piece 70 may be used, though those of ordinary skill in the art will recognize that other weld configurations may be used. In such an embodiment, the welded upstream axial fin 52 may be made from a different material than the outer sidewall 46. Stellite, inconel, or other similar alloys or materials, which generally are more resistant to solid particle erosion than the material of the outer sidewall 46 or outer ring 48, may be used. In other embodiments, the welded upstream axial fin 52 may be made from the same material as the outer sidewall 46 or outer ring 48.

As illustrated in FIG. 4, the upstream axial fin 52 may be attached to the outer sidewall 46, or in other cases (not shown), the outer ring 48, by mechanically connecting or peening the component into place. In this embodiment, a tapering or rectangular piece 80 may be used to form the upstream axial fin 52. The rectangular piece 80 may include a dovetail or hook 82 at one end, but it may also include other configurations that lend themselves to mechanical connection or peening. During installation, the hook 82 may be inserted into a dovetail or groove 84 in the outer sidewall 46. As known in the art, the outer sidewall 46 then may be peened at a location adjacent to the groove 86 such that the outer sidewall 46 is deformed and the hook 82 is mechanically locked within the groove 84. The outer sidewall 46 or outer ring 48 also may include a secondary, smaller groove (not shown) that aids in the mechanical deformation of the peening process.

The mechanically connecting or peening of the upstream axial fin 52 into place also would allow the upstream axial fin 52 to be made from a different material than that of the outer sidewall 46 or outer ring 48. Stellite, inconel, or other similar alloys or materials, which generally are more resistant to solid particle erosion than the material of the outer sidewall 46 or outer ring 48, may be used. In other embodiments, the mechanically connected or peened upstream axial fin 52 may be made from the same material as the outer sidewall 46 or outer ring 48. In addition, attaching the upstream axial fin 52 by mechanically connecting or peening may allow for the upstream axial fin 52 to be efficiently retrofitted into existing outer sidewalls 46 or outer rings 48 (or any of the other components that may define the upstream edge of the opening 38). In this manner, the upstream axial fin 52 may be added to a turbine in which significant solid particle erosion has occurred to prevent further erosion from occurring. Thus, the upstream axial fin 52 may be applied to an existing flowpath or to a new flowpath.

The downstream axial fin 58 may be formed by methods similar to those described above for the upstream axial fin 52. That is, the downstream axial fin 58 may be an integral part machined as part of the blade cover 20 or may be welded or mechanically connected or peened into place to an existing blade cover 20. The downstream axial fin 58 may be made from the same materials as described above for the upstream axial fin 52.

In operation, the seal guard 50 may provide a shield to deflect solid particle impurities from entering the opening 38. The seal guard 50 also may alter the flow characteristics around the opening 38 so that solid particle impurities are carried away from the opening 38. The solid particle impurities, thus deflected or carried away within the main flowpath, would not be able to come in contact with or erode the components of the seal 32 (and other turbine components in this area of the turbine) and the performance of the turbine would not be adversely affected by increased leakage. More specifically, the upstream axial fin 52 and the downstream axial fin 58 would significantly reduce the axial extent of the opening 38, which would reduce the number of solid particles entering the opening 38. Further, the upstream axial fin 52 and its tapering point 54 would replace the existing gradual curvature at the leading edge of the opening 38 that invites solid particles to enter.

In some embodiments, the upstream axial fin 52 may be used without the downstream axial fin 58. In such embodiments, the upstream axial fin 52 may be configured such that it spans a significant percentage of the opening 38. Further, as illustrated in FIG. 5, the upstream axial fin 52 may be used with a downstream groove 90. The downstream groove 90 may be a groove or recess within the blade cover 20. In such embodiments, the upstream axial fin 52 may span the opening 38 and terminated within the downstream groove 90.

Likewise, in alternative embodiments, the downstream axial fin 58 may be used without the upstream axial fin 52. In such embodiments, the downstream axial fin 58 may be configured such that it spans a significant percentage of the opening 38. Further, as illustrated in FIG. 6, the downstream axial fin 58 may be used with an upstream groove 94. The upstream groove 94 may be a groove or recess within the outer sidewall 46 or outer ring 48. In such embodiments, the downstream axial fin 58 may span the opening 38 and terminated within the upstream groove 94.

In other embodiments, the upstream axial fin 52 may overlap or almost overlap with the downstream axial fin 58, shown in FIG. 2. In such embodiments, the downstream axial fin 58 may be positioned slightly more outward radially than the upstream axial fin 52. Such an embodiment forces the solid particles to substantially weave through the overlapping or closely placed axial fins to reach the seal 32 and related components. However, given the relative radial positions of the axial fins and flow direction imparted upon the working fluid by the upstream axial fin 52, such movement by the solid particles is highly unlikely. With the number of solid particles flowing to the seal 32 being significantly limited, erosion to the seal 32 and neighboring components will be greatly reduced.

From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof. 

1. A system for preventing solid particle erosion in a turbine, the turbine including turbine blades that include a blade cover and an opening defined by a trailing edge of a nozzle and a leading edge of the blade cover, the system comprising at least one of an upstream axial fin positioned at the trailing edge of the nozzle and a downstream axial fin positioned at the leading edge of the blade cover.
 2. The system of claim 1, wherein the trailing edge of the nozzle comprises an outer sidewall.
 3. The system of claim 2, wherein the upstream axial fin comprises a fin that protrudes from the outer sidewall in a downstream direction.
 4. The system of claim 1, wherein the upstream axial fin extends in a substantially continuous circumferential manner.
 5. The system of claim 1, wherein the upstream axial fin comprises a fin that extends in an axial manner across at least part of the opening.
 6. The system of claim 1, wherein the downstream axial fin comprises a fin that protrudes from the blade cover in an upstream direction.
 7. The system of claim 1, wherein the downstream axial fin comprises a fin that extends in an axial manner across at least part of the opening.
 8. The system of claim 1, wherein the downstream axial fin extends in a substantially continuous circumferential manner.
 9. The system of claim 1, wherein the system includes both an upstream axial fin and a downstream axial fin.
 10. The system of claim 9, wherein the upstream axial fin and the downstream axial fin comprise approximately the same radial position and substantially span the axial distance of the opening.
 11. The system of claim 9, wherein the downstream axial fin is positioned slightly more outward radially than the upstream axial fin; and wherein the downstream axial fin and the upstream axial fin overlap axially.
 12. The system of claim 2, wherein the upstream axial fin comprises an integral part of the outer sidewall.
 13. The system of claim 2, wherein the upstream axial fin is attached to the outer sidewall by welding or peening.
 14. The system of claim 1, further comprising a downstream groove positioned in the leading edge of the blade cover; wherein the upstream axial fin spans the opening and terminates within the downstream groove.
 15. The system of claim 1, further comprising an upstream groove positioned in the trailing edge of the nozzle; wherein the downstream axial fin spans the opening and terminates within the downstream groove.
 16. A seal guard in a turbine, the turbine including a plurality of circumferentially spaced nozzles, a plurality of circumferentially spaced turbine blades that each include a blade cover, and an opening defined by a trailing edge of the nozzles and a leading edge of the blade covers, the seal guard comprising: an upstream axial fin positioned at the trailing edge of the nozzles that extends in a downstream direction across at least part of the opening or a downstream axial fin positioned at a leading edge of a blade cover that extends in an upstream direction across at least part of the opening.
 17. The seal guard of claim 16, wherein the system includes both the upstream axial fin and the downstream axial fin, and the upstream axial fin and the downstream axial fin comprise approximately the same radial position and substantially span the axial distance of the opening.
 18. The seal guard of claim 16, wherein the system includes both an upstream axial fin and a downstream axial fin; the downstream axial fin is positioned slightly more outward radially than the upstream axial fin; and the upstream axial fin and the downstream axial fin overlap axially.
 19. The system of claim 16, further comprising a downstream groove positioned in the leading edge of the blade cover; wherein the upstream axial fin spans the opening and terminates within the downstream groove.
 20. The system of claim 16, further comprising an upstream groove positioned the trailing edge of the nozzle; wherein the downstream axial fin spans the opening and terminates within the upstream groove. 